Three conductor planar antenna



July 10, 1962 Original Filed June 6, 1955 J. L. BUTLER THREE CONDUCTORPLANAR ANTENNA 2 Sheets-Sheet J Jesse L. Butler INVENTOR.

y 1962 J. L. BUTLER 3,044,066

THREE CONDUCTOR PLANAR ANTENNA Original Filed June 6, 1955 2Sheets-Sheet 2 '2 Jesse L. Butler INVENTOR.

3,044,666 THREE CUNBUCTOR PLANAR ANTENNA Jesse L. Butler, Nashua, NIL,assignor to Sanders Associates, Inc, Nashua, N.H., a corporation ofDelaware Original application June 6, 1955, Ser. No. 513,223, now PatentNo. 2,914,766, dated Nov. 24, 1959. Divided and this application Nov.18, 1959, Ser. No. 853,839

3 Claims. (Cl. 343-771) printed circuit configurations and are,moreover, bulky,

3,044,666 Patented July 10, 1962 ice insulating members support theconductors in spaced relation. Side conductive members connect the edgesof the outer conductors together to provide boundaries for suppressingthe extraneous modes of propagation. An

expensive and inflexible in relation to the needs of modern I microwaveengineering.

It is therefore an object of the invention to provide an improvedmicrowave antenna utilizing configurations readily adaptable to printedcircuit techniques.

A further object of the invention is to provide an improved antenna ofthe type described employing resonant dipole radiators.

A still further object of the invention is to provide an improvedantenna of the type described utilizing a plurality of resonant slotradiators.

It is a further object of the invention to provide an improved antennaof the type described including means for phasing resonant radiatingelements.

It is a still further object of the invention to provide an improvedantenna of the type described including means for varying the degree ofexcitation of resonant, radiating elements.

A still further object of the invent-ion is to provide an improvedantenna of the type described including means for suppressing extraneouspropagation modes.

Other and further objects of the invention will be apparent from thefollowing description of preferred embodiments, taken in connection withthe accompanying drawings.

In accordance with the present invention there is provided an antennawhich comprises the combination of a first elongated outer conductorproviding a ground plane and a second elongated outer conductorproviding a second ground plane. An elongated inner conductor of lesserWidth than the outer conductors is centrally disposed in insulatedspaced relation between the outer conductors. A resonant radiatingelement is disposed in the path of propagation. Discontinuity means aredisposed in the path of propagation to excite the radiating element.Side conductive means disposed less than a half wavelength apart M2 atthe operating frequency connect the sides of the outer conductorstogether adjacent their opposite edges to suppress extraneous modes ofpropagation.

In the preferred embodiment there is provided an antenna which comprisesthe combination of a first elongated, planar, outer conductor providinga first ground plane along an axis, and a second elongated, planar,outer conductor providing a second ground plane, parallel and inregister with the first ground plane. The conductors are less thanone-half of one wavelength wide at the operating frequency and so thinas to be incapable of selfend conductive member connects the sideconductive members and the outer conductors together enclosing an endthereof. A pair of elongated slots are formed in the side conductivemembers and are axially disposed adjacent the end. The slots areone-half of one wavelength long at the operating frequency. A resonantdipole element is connected to and extends from the center of the firstouter conductor a distance of one-quarter of one Wavelength from theend. A discontinuity conductive member is co-linear with the dipoleelement and connectsthe first outer conductor and the inner conductortogether. A second dipole element is co-linear with the first dipoleelement and is connected to and extends from the center of the secondouter conductor.

In a modification of the invention a plurality of elongated, resonantradiating slots are formed in the outer conductors and augularlydisposed relative to the direction of propagation. The slots in a givenouter conductor are separated by an integral number of Wavelengths atthe operatingv frequency. The slots are one-half of one wavelength longat the operating frequency.

In a further embodiment of the invention the slots have enlarged endportions to cause their elfective length to be one-half of onewavelength long at the operating fre quency and are disposedperpendicular to the direction of propagation. In one aspectof theinvention the enlarged .end portions have substantially a rectangularconfiguration. In another aspect of the invention, the enlarged endportions have substantially a circular configuration.

In a further modification of the invention the configuration of theinner conductor is so chosen as to increase the propagation path betweenslots and cause slots which are physically separated by less than anintegral number of wavelengths at the operating frequency to beefiectively, electrically separated by substantially an integral numberof wavelengths.

In another embodiment of the invention shunt slots are formed in theouter conductors and are longitudinally disposed alternately on oppositesides of the center line of the outer conductors. The slots on the sameside of the center of the outer conductors are separated byonewavelength at the operating frequency. Successive slots disposed oneither side of the center of the outer conductors are disposed one-halfof one wavelength apart at the operating frequency.

In still another embodiment of the invention a discontinuity isintroduced between the first outer conductor and the inner conductor toexcite resonant shunt slots which are formed in the side conductivemembers adjacent an end thereof.

the antenna in FIG. 1 taken along the lines 22.

FIG. 3 is a cross-section, partially schematic, view of the antenna inFIG. 1; Y

FIG. 4 is an isometric view, partially fragmentary, of an antennaembodying a modification of the invention;

.FIG. is a plan View, partially fragmentary, of an antenna embodying afurther modification, of the inven tion;

FIG. 6 is asectional view of the embodiment in FIG;

5 taken along the lines 6-6;

FIG 7 is a plan view, partially fragmentary, of still another embodimentof the invention;

FIG. 8 is a sectional View ofthe embodiment in FIG. I

7 taken along the lines 8--8;

"FIG. 9 is aplan view, partially fragmentary,- of a. modi fication ofthe embodiment of FIG. 4;

FIG. 10 is a plan view,fipartially fragmentary, of a modification of theembodiment of FIG. 7; 7

FIG. 11 is a plan view, partially fragmentary, of another embodiment ofthe invention; and

FIG. 12 is an isometric view, partially fragmentary of still anotherembodiment of the invention.

radiators are utilized is illustrated in FIG. 4. Resonant radiatingslots 12 are formed in the uppermost outer conductor and angularlydisposed at an angle a relative to the direction of propagation 2, asshown. Since the outer conductor 1 as shown is less than one-half of onewavelength'wide at the operating frequency, the slots 12 must beangularly disposed to obtain an efiective, electrical length one-half ofone wavelength M2 long at the operating frequency. The slots 12 arelongitudinally disposed a wavelength A apart at the operating frequency,where A is taken to be the propagation wavelength within the antenna.

In FIG. 5 and the sectional view of FIG. 6, the slots are shown withenlarged end portions 13a to cause the In each of the above figuresexcept the cross-sectional views, microwave energy is assumed to beintroduced from theleft as shown.

Referring now to the drawings, and with particular reference to FIGS. 1,2, and 3 a first, elongated, planar,

outer conductor 1 formed, for example, of copper foil .001 of an inchthiclc provides a first ground plane along an axis in the direction ofpropagation of the energy within the antenna as indicated at 2. Asecond, elongated, planar, outer conductor 3 provides a second groundplane parallel and in register with the first ground plane as shown. Theouter conductors, as shown, are less than one-half of one wavelengthwide M2 at the operating frequency. Here, M2 refers to the wavelength ofpropagated energy within the antenna as determined by the dione-quarterof one wavelength apart as shown.

In the embodiment of FIG. 9 the inner conductor 16 has a curvedconfiguration as shown, to increase the length of the propagation pathwithin the antenna and cause the slots 12 to be separated electrically afull wavelength it apart at the operating frequency, even thoughphysically they are disposed less than a wavelength apart. In FIG. 10'an antenna of the type described utilizing circularly enlarged slots 17physically disposed less than electric constant of the insulators which.support the conductors in spaced relation as is well-known in the art.

An'elongated, planar, inner conductor 4 is narrower than ene impregnatedFiberglas, support the conductors 1, '3, V

and 4 in the above-mentioned spaced relation.

The conductors and insulating members are laminated together, forexample, by suitable processes involvingthe use of a cupric coatedconductor as disclosed in a copending application, Serial No. 459,841,filedOctoberl, 1954, by Victor FiDahlgre'n entitled, Method of BondingCopper to Tri-fluoro-chloro-ethylene, A pair of longitudinally disposedside conductive members 6 con-.

nects the edges of the outer conductors 1 and 3 together, as shown, toprovide boundaries for suppressing extraneous modes of propagation. Anend conductive member 7 connects the side conductive members and theconductors 1, 3, and'4 together enclosing an end thereof as shown. Apair of elongated slots 8 are formed in the side conductive members 6and are axially disposed adjacent the end of the conductors as. shown.The slots are resonant and are electrically one-half of one wave lengthM2 long at the operating frequency. The exact length for resonance isdetermined experimentally and.

is somewhat less than the physical one-half of one wavelength w/Z infree space due to the shunt capacity efiect of the dielectric members 5.A resonant dipole element 9 is connected to and extends from the centerof the first outer conductor 1 and is disposed one-quarter of awavelength from the end. of the conductor 1 as shown. A discontinuityconductive member 10 is disposed colinear with the dipole element 9 andconnects the first outer conductor 1 and inner conductor 4 together. Asecond dipole. element -11, disposed co-linear with the first dipoleelement 9, is connected toand extends fromthe center of the second outerconductor 3 as shown. The dia wavelength apart are shown as used with acurved planar inner conductor 18 parallel to the outer conductors. Thecurved conductor 18 extends the propagation path within the antenna andeffectively, electrically separates the slots 17 by one wavelength A.

In FIG. 11 an embodiment of the invention is illus* trated in whichresonant slots 19 ars disposed successively on alternate sides of acenter line 21 of the outer condoctor 20. The slots areelectrically'ahalf wavelength M2 long at the operating frequency and successive slotsare displaced'one-half of a propagation wavelength apart as. shown."

In the embodiment of FIG. 12 a pair of slots 22 are shown disposed inthe side conductive member 23-. Another slot 24 is longitudinallydisposed oil the center line 26 of the outer conductor 25. A pair ofconductive, discontinuity members27 short circuit the outer conductor 25to the inner conductor 28 to excite the slots 22. The slots 22 and 24are each electrically one-half of a wavelength l\/2 long at theoperating frequency. The slot 24 provides its own discontinuity byvirtue of its position relative to the electric field in the typical TEMmode of propagation of the line. Relative to the direction ofpropagation of the energy within the antenna, the slots 22 and 24radiate broadside, the principal axis of radiation of the slots 22 beingperpendicular tothat .of the slot 24 when the slots 22 are separated byan integral number of wavelengths.

The dipole elements and 11 in the embodiment of FIG. 1 are symmetricallyexcited by microwave. energy which travels. through the slots 8 as shownin FIG; 3. The slots are formed in both side members 6 to balance theimpedances between the dipoles and ground as well as to provide maximumexcitation to the radiating dipoles. The slots 8 are' on the order ofone-eighth wavelength A/ 8 wide, which varies with the impedance of theantenna; hence, the slot width is a function of the impedance requiredfor proper termination of an input transmission line. The slots 8 arepreferably centrally disposed relative to the discontinuity member 10but may be varied in position to vary the degree of excitation of theresonant dipole radiating elements 9 and 11. Energy radiated by theslots 8 is plane-polarized perpendicular to the principal direction ofpropagation within the antenna. The dioles radiate omnidirectionally infree space in a principal plane parallel to the outer conductors 1 and3.

The conductors 1, 3 and 4 comprise a double ground plane transmissionline which characteristically prop-agates microwave energy in the TEMmode; i.e., the electric field distribution between the conductors 4 issymmetric and 180 degrees out of phase with the field between theconductors 3 and 4. Such a transmission line does not radiate withoutthe introduction of a discontinuity to disturb the symmetry of theelectric fields. The conductive discontinuity member connects the outercon ductor 1 to the inner conductor 4 to short circuit the electricfield therebetween at the point of highest intensity. Such adiscontinuity sets up a diiference of potential between the conductors 1and 3 which tends to initiate propagation in a different mode; e.g.,parallel plate or TE A discontinuity may also be effected by insertingmaterial between the conductors which is characterized by a dielectricconstant difiering from the insulating members 5. The side members 6 areseparated less than one-half wavelength M2. apart at the operatingfrequency to provide boundaries below cut-01f to suppress extraneouspropagation modes within the antenna.

In the embodiment of FIG. 4 a plurality of resonant, radiating slots 12are shown disposed within the outer conductor 1 at an angle a relativeto the principal direction of propagation of microwave energy within theantenna. Since the conductor 1 is less than one-half wavelength 2 wideand the slots 12. must be one-half wavelength M 2 long to be resonant,the slots are angularly disposed as shown. The angle a may be varied foreach slot to vary the degree of excitation in accordance with theexpression:

( E=A sin a Where E=degree of excitation and A=maximum energy availableto each slot.

For broadside radiation, along an axis perpendicular to the conductor 1,the slots 12 are separatedone-Wavelength in the direction ofpropagation. For end fire radiation, that is, in a direction parallelWith the principal direction of propagation within the antenna, theslots are separated one-half wavelength apart. Since the wavelength inthe antenna is a function of the propagation constant and, hence, thedielectric constant of the insulators, the phase of the slots may bevaried to vary the principal direction of radiation in free space byintroducing dielectric materials with difiering dielectric constants.

Slots may be formed in the outer conductor 3 corresponding to and inregister with the slots 12. In this case, the propagation fields withinthe antenna are symmetric, the slots introducing no discontinuity todisturb the TEM mode symmetry. The side members 6 may then beeliminated.

The slots may be oriented perpendicular to the principal direction ofpropagation within the antenna by enlarging the end portions as in FIGS.5 and 7 to cause the slots to be effectively, electrically one-halfWavelength long M2.

Slots asymmetrical with the slots 12 may be formed in the conductor 3.Since the side members 6 suppress extraneous modes of propagation whichmay tend to arise, the radiation relative to the conductor 1 issubstantially independent of the radiation relative to the conductor 3.Thus, radiation at a principal angle of 45 degrees may take placerelative to the conductor 3, while radiation at 90 degrees isefiectedrelative to the conductor 1. As is well-lmown in the art,increased directivity of radiation is provided proportional to thenumber of slots.

The angularly disposed slots tre termed hybrid in the art asdistinguished from being in series or perpendicular and in shunt orparallel relative to the principal direction of propagation within theantenna. Where slots are formed in both outer conductors 1 and 3,dielectric materials of diiierent constants may be used to effect thephasing. Thus, an insulating member with a dielectric constant of 2.5may be used between the conductors 1 and 4 while an insulating memberhaving a dielectric constant of 2.0 may be used between the conductors 3and 4.

For maximum excitation, the slots are perpendicularly disposed as inFIGS. 5 and 7. It a rectangular slot less than one-half Wavelength longM 2 is used, an insert of insulating material beneath the slotcharacterized by a higher dielectric constant relative to the insulatingmembers 5 may be utilized to effectively increase its electrical lengthto one-half wavelength. Similarly, the slots 13 and 14 may haveenlarged, substantially rectangular, end portions 13a as in FIG. 5 orsubstantially circular end portions 14:: as in FIG. 7.

As a practical matter, conductive rods 15 as shown in FIGS. 7 and 8 areused to provide mode suppression. The rods 15 are longitudinallydisposed less than onequarter wavelength apart and transversely disposedless than one-half wavelength apart as shown.

The configuration of the ii'mer conductor may be so chosen as to varythe degree of excitation of the resonant slots, the phasingtherebetween, or both. Thus, in FIG. 9, the inner conductor is curved asshown to extend the propagation .path between the slots 12. The angle ,8between the inner conductor 16 and the slots 12 as shown determines thedegree of excitation of the slots.

Varying the configuration of the inner conductor of prior art coaxialtransmission line to vary the path of propagation has beenunsuccessfully attempted. Excessive capacitive coupling between adjacentloops defeats the purpose of providing a longer path by short circuitingthe loops. Here substantially no capacitive coupling is encounteredwithin the inner conductor 16, since its edges present a negligiblesurface area and the conductor is planar.

In the embodiment of FIG. 10, the configuration of the innerconductor'18 is so chosen as to extend the propagation path between theslots 17 without changing the excitation to each slot. Here theconductor 1% is perpendicular to the slots 17 atintersectionstherebetween as shown. Conversely, the configuration of theconductor 18 may be modified to vary the excitation to each slot withoutsubstantially extending the propagation path between the slots.

In the embodiment of FIG. 11 the slots 19 are succesv sively alternatelydisposed on either side of the center line 21 of the conductor 20 asshown. The field distribution within the antenna decreases exponentiallyfrom the center (as illustrated by R. M. Barrett in his articleentitled, Etched Sheets Serve As Microwave Components, Electronics, June1952, page 115, FIGURES 1 and 2). In prior art, conventional,waveguides, the electric field intensity decreases sinusoidally. Herethe slots are located closer together relative to the center line 21than is possible in such prior waveguides for a given degree atexcitation. Prior art coaxial line is incapable of this type of slotexcitation since the transverse equipotential electric intensitydistribution is circularly symmetric.

In the antenna of FIG. 1, for operation, forexample, at 10,000megacycles, X-band, the conductors 1 and 3 are 7 of an inch wide by .001of an inch thick; the conductor -l is /s o-f an inch Wide by .001 of aninch thick; the insulators 5 are of an inch thick; the dipole elements.26 of an inch long by .020 of an inch in diameter; and the slots 8 are.57 of an inch long by .1 of an inch Wide.

The antenna of the present invention combines the advantages of priorart coaxial and waveguide transmission line devices in a configurationreadily adaptable to printed circuit techniques. The present inventionis broadly applicable to every area of radio signaling.

While there has been hereinbefore described what are at presentconsidered preferred embodiments of the invention, it will be apparentthat many and various changes and modifications may be made withrespectrto' the embodiments illustrated, Without departing from thespirit of the invention. It will be understood, therefore, that all suchchanges and modifications as fall fairly within the scope of the presentinvention, as defined in the appended claims, are to be considered as apart of the present invention;

What is claimed is:

1. An antenna comprising the combination of a first elongated, outerconductor providing a ground plane; a second elongated, outer conductorproviding a second ground plane, said conductors being less thanone-halt of a wavelength Wide at the operating frequency; anonlinearelongated inner conductor of lesser width than said outerconductors centrally disposed in insulated spaced relation between saidouter conductors; side conductive means connecting the sides of saidouter conductors together at their opposite edges to suppress extraneousmodes of propagation; and elongated, resonant, radiating slots spacedeffectively, along the length of the inner conductor, a Wavelength apartat the operating frequency formed in said first outer conductor, alinear dimension of said slot forming an acute angle with respect tosaid inner conductor and. being substantially effectively one-halfwavelengthlong at the operating frequency, to provide radiation along anaxis perpendicular to said first outer conductor.

2. An antenna comprising the combination of a first elongated, outerconductor providing a ground plane; a second elongated, outer conductorproviding a second ground plane, said conductors being less thanone-half of a wavelength wide at the operating frequency; an elongated,planar inner conductor of lesser width than said outer conductors,centrally disposed in insulated spaced relation between said outerconductors; side conductive means connecting the sides of said outerconductors together at their opposite edges to suppress extraneous modesof propagation; and a plurality of elongated, parallelogram shaped acuteangularly disposed with respect to said inner conductor, resonant,radiating slots formed in said'first outer conductor and angularlydisposed less than an integral number of wavelengths apart at saidoperating frequency, the configuration of said inner conductor being sochosen as to increase the propagation path Within said antenna betweensaid slots and cause them to be effectively electrically an integralnumber of wavelengths apart.

3. An antenna comprising the combination of a first flat, elongatedouter conductor providing a ground plane along an axis; a second flat,elongated outer conductor providing a second ground plane parallel andin register With said first ground plane, said conductors being lessthan one-half of one Wavelength Wide at the operating frequency and sothin as to be incapable of self-maintaining their configuration; a fiatelongated inner condoctor of lesser Width than said outer conductors andcentrally disposed in parallel with and in spaced relation between saidouter conductors; elongated dielectric insulating members supportingsaid conductors in said spaced relation; a pair of longitudinallydisposed side conductive members connecting the edges of said outerconductors together to provide boundaries for suppressing extraneousmodes of propagation; ands-a plurality of elongated slots formed in saidfirst outer conductor and angularly disposed with regard to thedirection of propagation, said slots being one-half of one wavelengthlong and separated by one wavelength at the operating frequency.

References Cited in the tile of this patent UNITED STATES PATENTS2,465,245 Mabry Mar. 22, 1949 2,602,856 Rumsey July 8, 1952 2,654,842Engelmann 2 Oct. 6, 1953 2,756,421 Harvey et a1. July 24, 19562,761,13'; Van Atta Aug. 28, 1956 2,840,818 Reed et a1. June 24, 19582,914,766 Butler Nov. 24, 1959 FOREIGN PATENTS 1,014,722 France June 18,1952 OTHER REFERENCES Microwave Antenna Theory and Design, by Silver,1949, pp. 226-229, 291-292,.296, 298.

